CONCISE COMMUNICATION BJD British Journal of Dermatology Evidence for a polygenic contribution to androgenetic alopecia S. Heilmann, 1,2 F.F. Brockschmidt, 1,2 A.M. Hillmer, 3 S. Hanneken, 4 S. Eigelshoven, 5 K.U. Ludwig, 1,2 C. Herold, 6 E. Mangold, 1 T. Becker, 6,7 R. Kruse, 8 M. Knapp 7 and M.M. N€ othen 1,2 1 Institute of Human Genetics, University of Bonn, Bonn, Germany 2 Department of Genomics, Life and Brain Centre, University of Bonn, Bonn, Germany 3 Genome Technology and Biology, Genome Institute of Singapore, Singapore, Singapore 4 Department of Dermatology, University of D€ usseldorf, D€ usseldorf, Germany 5 Private Dermatology Practice, Solingen, Germany 6 German Centre for Neurodegenerative Diseases (DZNE), Bonn, Germany 7 Institute of Medical Biometry, Informatics, and Epidemiology, University of Bonn, Bonn, Germany 8 Private Dermatology Practice, Paderborn, Germany Correspondence Stefanie Heilmann. E-mail: sheilman@uni-bonn.de Accepted for publication 11 May 2013 Funding sources The study was supported by Life & Brain GmbH and Alfried Krupp von Bohlen und Halbach-Stiftung. Conflicts of interest None declared. DOI 10.1111/bjd.12443 Summary Background Male pattern baldness (androgenetic alopecia, AGA) is a highly herita- ble trait and the most common form of hair loss in humans. Eight genome-wide significant risk loci for AGA have been identified. Objectives To determine whether a polygenic component contributes to the genetic risk for AGA. Methods This study used a German case–control sample for AGA, which comprised 581 severely affected patients and 617 controls, to determine the contribution of polygenic variance to AGA risk. The sample was divided evenly into discovery and test samples. An additive polygenic risk score was calculated from risk alleles with increasingly liberal P-values in the discovery dataset, which was then used to test for the enrichment of AGA risk score alleles in the independent test sam- ples. Results The polygenic score analysis provided significant evidence for a polygenic contribution to AGA where the amount of variance explained was 1Á4–4Á5%. Conclusion This study provides evidence for the specific contribution of a poly- genic component to the overall heritable risk for AGA. To some degree, the poly- genic architecture of AGA might reflect the complexity of the biological pathways involved. Further analyses and strategies that complement conventional genome-wide association studies are needed to identify these factors. These may include pathway-based analyses, the analysis of functional candidate genes and tests for epistatic effects with known loci. What’s already known about this topic? • Androgenetic alopecia is a highly heritable trait and the most common form of hair loss in humans. Eight genetic susceptibility loci have been linked with male pattern baldness. What does this study add? • This study provides molecular genetic evidence that a polygenic component con- tributes to the individual risk of developing androgenetic alopecia. Male pattern baldness (androgenetic alopecia, AGA; OMIM 109200, OMIM 300710, OMIM 612421) is a highly heritable trait that is characterized by a progressive loss of hair from the scalp. 1 Hair loss may commence during puberty, affecting © 2013 British Association of Dermatologists British Journal of Dermatology (2013) 169, pp927–930 927